text: After the DNA-gelatin mixture preparation, the mixture is pipetted onto a slide surface and the slide is placed in a covered petri dish. A desiccant is added to the dish to dry up the solution. Finally, cultured cells are poured into the dish for plasmid uptake. However, with the invention of different types of microarray printing systems, hundreds of transfection mixes (containing different DNA of interest) may be printed on the same slide for cell uptake of plasmids. There are two major types of microarray printing systems manufactured by different companies: contact and non-contact printing systems. 
  An example of a non-contact printing system is the Piezorray Flexible Non-contact Microarraying System. It uses pressure control and a piezoelectric collar to squeeze out consistent drops of approximately 333 pL in volume. The PiezoTip dispensers do not contact the surface to which the sample is dispensed; thus, contamination potential is reduced and the risk of disrupting the target surface is eliminated. An example of a contact printing system is the SpotArray 72 (Perkin Elmer Life Sciences) contact-spotting system. Its printhead can accommodate up to 48 pins, and creates compact arrays by selectively raising and lowering subsets of pins during printing. After printing, the pins are washed with a powerful pressure-jet pin washer and  vacuum-dried, eliminating carryover. Another example of a contact printing system is the Qarray system (Genetix). It has three types of printing systems: QArray Mini, QArray 2 and QArray Max. After printing, the solution is allowed to dry up and the DNA-gelatin is stuck tightly in position on the array.